The objective of the proposed project is the anatomical analysis of corticothalamic and thalamocortical connections of the thalamic pulvinar complex in the cat. The aim of this analysis is the identification of the specific populations of thalamic neurons which constitute the anatomical substrates for interactions between visual cortex and association cortex. Autoradiography will be employed to demonstrate projections of cortical areas identified by electrophysiological recording. Thalamic neuronal populations recipient of specific cortical inputs will be identified by analysis of the topographic distribution of cortical projections. The distribution of projections back onto cortex from the identified populations of thalamic neurons will be similarly studied with autoradiographic tracing methods. Electron microscopy will be employed to evaluate the influence of the cortical projections which converge on given populations of thalamic neurons.